The bibliographic correlations search screen is designed to assist catalogers in assigning classification numbers. It does
this by looking at Library of Congress bibliographic data and determining the most common use of a given classification
number, subject heading or name heading. The correlations search screen offers multiple access points for answering these
types of questions:
- What are the subject headings most frequently used with a specific LC classification number?
- What are the LC classification numbers most frequently used with a specific subject heading?
- What are the LC classification numbers most frequently used with a specific Dewey or National Library of Medicine classification number?
Unlike LC authority subject and name headings, all headings in the correlations system include any subdivisions that were
applied in the bibliographic records. You do not need to enter any dash characters (--) between subdivisions to
locate a particular combination of subject heading and its subdivisions.
Use the Reset button to clear the correlation screen whenever you want to start a new search.
How it Works
Bibliographic correlations are created by processing the the Library of Congress bibliographic database, extracting
particular fields and making note of how many times certain combinations of fields appear together in the same record.
Not all records or data elements are used. The restrictions include:
- Any records with an abbreviated, partial or minimal encoding are skipped entirely. In other words, any records with a
leader/17 value of '3', '5', or '7'.
- Visual materials (leader/06) are not included in any correlations that involve LC classification numbers. However,
visual materials are included for National Library of Medicine and Dewey numbers.
- Only the first valid LC classification number that was assigned by LC is used in correlations.
- Only the first valid NLM classification number that was assigned by NLM is used in correlations.
- Only the first valid Dewey classification number that was assigned by LC is used in correlations.
Subject Heading Correlations
Only the first topical subject heading field (650 or 651) in each record is used to create subject
Subject Heading (Including Names) Correlations
The first 6xx field from each record is used to create these correlations.
Name as Creator Correlations
The 1xx field from each record is used to create these correlations.
When you search any of the correlations, the list that is returned is presented as a "top ten" list (i.e. the ten most
common subjects for a given classification number or the ten most common classification numbers for a particular subject).
Each result includes a number in parentheses that indicates the number of times that combination was found in the
Because the system only returns ten correlations per subject, name or classification number, you may not find the particular
combination you expected. It doesn't mean it is not in the database; just that it didn't make the "top ten" list. Also
keep in mind that the eleventh entry (not shown) may have the same number of correlations as the tenth (the last entry
that is displayed).
How to Search
Input the classification number or heading you have a question about, select the type of correlation you want to perform
and press Enter or click on the Search button. When inputting headings, you don't have to input dashes when
searching for subdivisions.
For on-screen search tips that describe each of the correlations, click on the Search tips link under Search
type input box. This link will not be available if you have search results on your screen. In that case, click on
the Reset button to clear the search screen and then click on Search tips.
In the display of correlation search results, all of the headings and LC classification numbers are formatted as
links that open a new window or tab with the appropriate LCSH, LCNH or LC class number browser.
For a general information on searching in ClassWeb, please refer to the following help page:
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